This invention relates generally to systems and methods employing a charge coupled device (CCD) and particularly to such a system and method for detecting blemishes on the screen of a kinescope.
CCDs are used in conjunction with an optical lensing system which focuses the light from the object being investigated onto the CCD. Varying amounts of light on the individual pixels within the CCD charge the pixels to different levels proportional to the incident light. The optical information from the object is, therefore, available in analog form across the pixels of the CCD array. The analog information is then shifted out of the CCD and converted into digital form and stored in a digital memory where the various characteristics of the object can be checked or tested by the proper manipulation of the digital information. The individual pixels within a CCD array typically are closely spaced and are arranged horizontally in rows and vertically in columns so that a given CCD imaging device provides a fixed number of pixels of information. As an example, the SID52501 CCD presently available from RCA corporation has 320 vertical columns of pixels and 512 horizontal rows of pixels. Accordingly, the information is read out from the CCD and stored in 320 vertical columns and 512 horizontal rows.
Charge coupled devices have several characteristics which make them advantageous in imaging. CCDs are small and rugged and have closely spaced pixels and accordingly, are useful in applications requiring precise measurements. Additionally. a CCD receives an image by the direct reception of energy without being scanned, and stores the received data until the data are transferred to a storage device. Accordingly, a CCD can image a device which develops an image by scanning without concern for the scanning rate of the device being imaged. Also, the data received from the CCD can be processed by simple comparison or detection techniques so that the voluminous and time consuming sampling techniques ordinarily required for processing data from a scanned image are not required. For this reason, CCDs are advantageous in systems for testing color television kinescopes for blemishes and convergence.
The instant invention utilizes these advantages by the provision of a CCD based blemish detection system and method wherein the charge received by each pixel of the CCD is compared with the average charge received by all immediately adjacent pixels to provide a blemish signal when the comparison exceeds a preselected threshold.